Gas Turbine Exhaust Energy Impacts on Achievement of and Times to Catalyst Activation Temperatures

摘要

Recently combined cycle gas turbine (GT) power plants have been designed to be utilized more often as load followers to compensate for the unpredictability of various renewables (e.g., wind and solar), rather than base-loaded plants, with the potential for more frequent daily startups and shutdowns (in addition to faster and more numerous ramping events). As a result, startup (and to a lesser extent, shutdown) emissions are significant contributors to total annual emissions budgets (e.g. total tons per year, TPY). Nitrogen oxide (NOx) emissions are often higher during startups as the selective catalytic reduction (SCR) catalyst can take some time to reach the approximate minimum operating temperature of 425 °F (218 °C) required to initiate ammonia injection for NO_x control. Carbon monoxide (CO) emissions are also much higher at lower loads (during startups), even with the presence of an oxidation catalyst, which takes time during a startup to reach its approximate minimum operating temperature of 300 °F (149 °C). This paper will discuss the issues related with the time required for the SCR and oxidation catalysts to reach their optimal normal operating temperatures. Actual operating plant "Cold" and "Hot" startup data will be discussed and compared, as will startups at different ramp rates (MW/min). In addition, this paper presents a 'typical' SCR warm-up scenario based on GT exhaust gas energy output, heat recovery steam generator (HRSG) metal heat "consumption" (from vendor data), and heat energy required to warm up the SCR catalyst. Lastly, this paper investigates options for reducing SCR and oxidation catalyst warm up times to operating temperatures.